What is the effect of increasing the thickness of an insulating material on heat transfer?
A Increases heat transfer
B Decreases heat transfer
C No effect
D Changes thermal conductivity
Increasing the thickness of an insulating material increases its resistance to heat flow, thereby decreasing the rate of heat transfer. Insulation works by reducing the thermal conductivity, and thicker materials offer more resistance to heat flow.
Which of the following materials is typically used for high-performance heat exchangers?
A Copper
B Steel
C Glass
D Aluminum
Copper is commonly used in heat exchangers due to its high thermal conductivity, which allows it to efficiently transfer heat. It is also corrosion-resistant, making it suitable for long-term use in heat transfer applications.
What role do fins play in heat exchangers?
A Reduce temperature gradient
B Increase heat flux
C Increase surface area
D Decrease thermal resistance
Fins are used to increase the surface area available for heat exchange in heat exchangers. A larger surface area allows for better heat dissipation or absorption, improving the overall heat transfer efficiency.
What type of heat transfer occurs when a person feels warm from sunlight?
A Radiation
B Convection
C Evaporation
D Conduction
Radiation is the mode of heat transfer that does not require a medium. Sunlight transfers heat through electromagnetic waves, which can travel through the vacuum of space and warm a person on Earth.
How does increasing the fluid velocity affect convective heat transfer?
A No effect
B Makes heat transfer unstable
C Increases heat transfer
D Decreases heat transfer
Increasing the velocity of the fluid increases the rate of convective heat transfer. Faster-moving fluid can carry more heat away from the surface, improving the overall heat exchange rate.
What is the main purpose of insulation in thermal systems?
A Increase heat flow
B Reduce heat transfer
C Increase fluid velocity
D Control temperature gradient
Insulation reduces the transfer of heat between two systems, helping maintain the desired temperature in a thermal system. It works by providing resistance to heat flow, thus improving energy efficiency.
Which heat transfer mode involves the movement of molecules in a material?
A Conduction
B Evaporation
C Conduction
D Radiation
Conduction is the transfer of heat through a material by the movement of molecules. In solids, heat is transferred from the high-temperature region to the low-temperature region as particles vibrate and collide.
In a heat exchanger, what does the heat transfer rate depend on?
A Fluid viscosity
B Heat source temperature
C Temperature difference
D Material density
The heat transfer rate in a heat exchanger is directly proportional to the temperature difference between the two fluids. A larger temperature difference increases the rate at which heat is transferred between the fluids.
What is thermal resistance in heat transfer?
A Heat absorbed by the material
B Rate of temperature change
C Heat released by the material
D Opposition to heat flow
Thermal resistance is the property of a material that resists the flow of heat. The higher the thermal resistance, the slower the heat transfer. It is inversely proportional to thermal conductivity and thickness.
Which material property affects how much heat a material can store?
A Thermal conductivity
B Specific heat
C Fluid velocity
D Surface area
Specific heat is the amount of heat required to raise the temperature of a unit mass of a material by one degree Celsius. Materials with high specific heat can store more heat before their temperature rises significantly.
What is the principle behind the operation of a heat pipe?
A Thermal expansion
B Latent heat transfer
C Radiation
D Conduction
Heat pipes operate by utilizing latent heat transfer. A liquid inside the pipe evaporates at the hot end, and the vapor travels to the cooler end, where it condenses, transferring heat in the process.
How does increasing the surface area of a material affect its heat transfer rate?
A Increases heat transfer
B Increases temperature gradient
C No effect
D Decreases heat transfer
Increasing the surface area allows more heat to be transferred between the material and the surrounding fluid. This is especially important in heat exchangers, where larger surface areas facilitate better heat exchange.
Which of the following is a common method to reduce heat loss in buildings?
A Reducing material thickness
B Increasing air circulation
C Using insulation
D Using metal walls
Insulation is the most common method used to reduce heat loss in buildings. It creates a barrier that resists the flow of heat, keeping the temperature inside stable and reducing energy consumption for heating or cooling.
What happens when a material’s thermal conductivity increases?
A No effect on heat flow
B Material becomes a better insulator
C Heat flow decreases
D Heat flow increases
Thermal conductivity refers to the ability of a material to conduct heat. As thermal conductivity increases, the material can transfer heat more efficiently, resulting in an increase in heat flow through the material.
In which process is latent heat involved?
A Freezing
B Boiling
C Condensation
D All of the above
Latent heat is involved in phase changes such as freezing, boiling, and condensation. It refers to the heat absorbed or released during a phase change, without a change in temperature, such as when liquid turns into gas during boiling.